MS Thesis Presentation by Janine Johnson
Tuesday, November 2, 2004
(Dr. Jianmin Qu, Chair)
"Thermomechanical Failure of Solid Oxide Fuel Cells (SOFCs)"
A possible solution of our societies’ growing energy needs is the use of planar oxide fuel cells (SOFC). A fuel cell uses electrochemical interactions to produce a voltage output, and a solid oxide cell consists of two porous ceramics (anode and cathode) through which flows the fuel and exhaust. These ceramics are bonded to a solid electrolyte layer across which the electrochemical reactions can take place. However, in a planar cell, external constraints, high operating temperatures, and thermal mismatch can cause sudden and unexpected mechanical failure. Since fracture testing can be both expensive and limited in scope, and analytical solutions are extremely complicated, it is necessary to create other methods to help in crack growth analysis. Therefore the fracture caused by thermal mismatch must be predicted computationally, using finite element methods, for planar SOFCs to reach their potential in commercial environments.
The research used finite modeling and classical fracture mechanics to investigate
three dimensional fractures of several types such as, interfacial, curvilinear,
and thermally induced. Initially a description of planar fuel cells is given
and thermal mismatch was introduced as the primary cause of fracture. From
this point on the body of the paper seeks to “build” a method
to analyze three-dimensional models using classical fracture mechanics. The
process starts by using beam theory too examine processing defects during
sintering of the electrolyte onto the anode. Next crack growth is examined
using a two dimensional finite element models. Finally, the research culminates
in the use of a multi step process to study fracture three dimensionally.
The overall result will be a comprehensive fracture measurement, not available
commercially, that can be used by leaders of the fuel cell industry to predict
mechanical failure of SOFCs.